Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
Particle in Cell simulations of RF and DC break down
HGF-Junior research group “COMAS”:
Study of effects on materials in contact with plasma, either with fusion or
low-temperature plasmas;
Development of computational multi-scale tools
Konstantin Matyash, Ralf Schneider
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
Particle in Cell model
0
1
E
x
dxv
dtdv q
E v Bdt m
1 1
0
x yx yS x x x and y y
EE
E
E
ii
i
qS x x
x y
t
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC simulation: RF capacitive discharge
potential
Parallel plate RF discharge (Univesity of Greifswald)fRF = 13.56 MHz , RF peak-to-peak voltage ~ 200 -1600 V
Gas : Oxygen, pressure p = 1 - 100Pa, electron density ne ~ 109 - 1010 cm-3
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC simulation: RF capacitive discharge
electron parallel velocity distribution 10 Pa, 250 VElectron and O2
+ density, 109 cm-3
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC simulation: RF capacitive discharge
electron-impact ionization rate simulation
C.M.O. Mahony et al., Appl. Phys. Lett. 71 (1997) 608.
double peak structure due to sheath reversal
653.3 nm excitation rate experiment
0 20 40 60 80 100 120 1400
2
4
6
8
10
n'ei , cm-3c-1
time, ns
Y, m
m
0
1.2E16
2.4E16
3.6E16
4.8E16
6E16
7E16
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
Particle-in-Cell code applications
D iv IIb
outerdiverto rpla te
inne rd ive rto r
p la te
Q M BS i-w a fe r
L a ngm uirprobe
roo fba ffle
2
4
6
8
816
2432
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Wall
Y, LdX, Ld
ne, 1010 cm-3
0 16 32 48 645x1010
5x1011
5x1012
5x1013
5x1014
n, cm-3
Y, ld
nH
nCH
4
nCH
3
nCH
2
nCH
nC
ECR plasma
Recycling in SOL
Parasitic plasma under AUG divertor
ne ~ 1010 cm-3
nn ~ 1014 cm-3
Te ~ 2 eV
ne ~ 1013 cm-3
nn ~ 1014 cm-3
Te ~ 10 eV
Plasma originated by photoionisation or photoeffect !
Plasma detected below roof baffle of Div IIb
Typical parameters:4*108 < ne < 7*1011 cm-3
5 < Te < 15 eVScaling: ne ~ Radiation2.7*Particles_flux0.7
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
Particle-in-Cell code applications
Dusty plasmas and plasma crystals
0 8642
X, D
0
2
4
6
8
Z, D
0 8642
0 24 86
30
28
26
X, D
Y, D
32
Ion trajectories close to the dust grain
Potential close the dust grain
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: DC discharge
Species included: e-, Cu+,Cu
Collisions:
Coulomb collisions for the (e-,e-), (Cu+,Cu+) and (e-, Cu+) e- + Cu => e- + Cu electron - neutral elastic collision e- + Cu => 2e- + Cu+ electron impact ionizationCu+ + Cu => Cu+ + Cu charge exchange and momentum transfer Cu + Cu => Cu + Cu elastic collisions
Simplistic surface interaction model:
• each Cu+ ion hitting electrode surface sputters
the Cu atom with probability 100% • each electron hitting the electrode surface
sputters the Cu atom with probability 1%. • each Cu atom hitting surface is reflected back
• electrodes material is Copper.
• the constant electron thermo-emission current Ieth = 2.35*106 A/cm2 from the cathode is assumed.
• the constant flux of evaporated copper atoms from the cathode ICu = 0.01Ieth /e is assumed
L = 20 mUa = +10 kV
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: DC discharge
Start-up phase of the discharge (the first 0.7 ns )
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: DC discharge
Simulated time 18 ns
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: DC discharge
Discharge current to anode
Main results:• Cu atoms evaporated from cathode are
ionized by the electrons accelerated in the
gap, creating e-, Cu+ plasma
• The flux of the plasma particles to the
electrodes enhances the sputtering, increasing
the concentration of the Cu atoms in the gap
• The plasma space charge start to influence the
external electric field in the gap when the
Debye length becomes smaller then the
electrode spacing.
• Electric field is concentrated in sheath ~8 Del
02e
Dee
kTn el
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: DC discharge
Cu+ flux energy composition at the cathode Cu flux energy composition at the cathode
Maximum energy corresponds to sheath potential dropLower enrery part is populated by collisions with neutrals
High energy neutrals due to charge exchange
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: RF discharge
Simulated time ~18 ns
Here frames are taken at 13/12TRF , so one can see RF dynamics
Same geometry and the model as for DC case,
only now right electrode is powered with RF voltage URF = 10 kV, fRF= 11.75 GHz
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: RF discharge
Discharge current to powered electrode
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
PIC modeling of arcing: RF discharge
Cu+ flux energy composition at the powered electrode
Cu flux energy composition at the powered electrode
more results at http://www.ipp.mpg.de/~knm/CERN/spark2.html
Max-Planck Institut für Plasmaphysik, EURATOM Association, 17491 Greifswald, Germany
Towards the integrated modeling of arcing
Particle-in-Cell modeling of arcing
• electric field concentrated in sheath
• triggered by electron field emission
• fluxes of plasma particles increase emission from the electrodes
Integrated Particle-in-Cell and Molecular Dynamics modeling of arcing
• energetic particles create surface damage
• explains experimentally observed cluster emission
• scaling studies on the way
• CERN PhD student position for Helga Timko (starting next year)
Thank you!